Porcess of vulcanizing rubber containing bis-alpha-methylbenzyl-substituted peenol monosulfides and resulting products



United States Patent PORCESS OF VULCANIZING RUBBER CONTAIN- ING BISALPHA METHYLBENZYL SUBSTI- TUTED PHENOL MONOSULFIDES AND RE- SULTINGPRODUCTS Harry E. Albert, Lafayette Hill, Pa., assignor to The FirestoneTire & Rubber Company, Akron, Ohio, a corporationof Ohio No Drawing.Continuation of application Serial No. 400,347, December 24, 1953. Thisapplication April 11, 1957, Serial No. 652,105

14 Claims. (Cl. 260-810) This invention relates to antiozone agentswhich inhibit or prevent the deterioration of natural rubber by ozone.

These agents are bis-2,4-disubstitnted phenol sulfides, one or both ofthe substituents being alpha-methylbenzyl groups. If only onesubstituent is an alpha-methylbenzyl substituent, the other is an alkyl,cycloalkyl, or aralkyl group containing up to nine carbon atoms. Therecan be two methyl groups on the alpha carbon of the benzyl substituent.I

Oxygen and ozone both have a harmful effect on rubber, but the efiect ofeach is diiferent, and compounds which inhibit or prevent the harmfulefiect of one are not necessarily effective in stopping the harmfulefiect of the other.

Crabtree and Kemp in an article in Industrial and Engineering Chemistry,vol. 38, starting at page 278 (1946), explain the diiference in theaction of oxygen and ozone. The light-catalyzed oxidation which occursduring outdoor exposure forms a skin and crazed appearance over theexposed surface of the rubber. Ozone, even in very low concentration,attacks stretched rubber only (C. H. Leigh-Dugmore, Rubber Age andSynthetics, November and December 1952), and forms cracks perpendicularto the direction of stretch, and such cracking can occur in the absenceof light.

As a matter of fact, practically all commercial rubber antioxidants arewithout effect in inhibiting deterioration caused by ozone. Thealpha-methylbenzyl-substituted phenol monosulfides of this invention donot absorb or act directly on the ozone, but have some unknown action inpreventing the cracking which is associated with ozone exposure instretched natural rubber.

Natural rubber is used in the manufacture of the whitesidewalls oftires. The cracking of such sidewalls has long been a problem. It isoften very extensive, and because of the color of the sidewall, it isvery noticeable. It is a primary object of this invention to provideantiozone agents which prevent such cracking without discoloring thesidewall. However, the antiozone agents of this invention are notlimited to that use but may beemployed in black sidewalls, treads,thread and other latex products, and other rubber products.

Tires are stressed when inflated. While a tire is at rest it isstretched statically, and on a moving vehicle it is stretcheddynamically. Some of the antiozone agents are more effective in statictests and others are more effective in dynamic tests. Antiozone agentseffective under both conditions will be desired for tires, but for otherrubber products an antiozone agent which does not meet both tests may beused.

The inhibitors of this invention include, for example:

Bis-2-alpha-methylbenzyl-4-methylphenol monosulfideBis-2-a1pha-methylbenzyl-4-isopropylphenol monosulfideBis-2-alpha-methylbenzyl 4-sec.butylphenol monosulfideBis-2-alpha-methylbenzyl-4-t-butylphenol monosulfideBis-2alpha-methylbenzyl-4-sec.amylphenol monosulfide 2,849,517 PatentedAug. 26, 1958 ice Bis-'2'-alpha-rnethylbenzyl-4-n-heptylphenolmonosulfide Bis 2-alpha-methylbenzyl-4-tt-octylphenol monosulfideBis-Z-alpha, alpha-dimethylbenzyl-4-methylphenol monosulfideBis-Z-methy1-4-alpha-methylbenzylphenol monosulfideBis-2-isopropyl-4-alpha-methylbenzylphenol monosulfideBis-Z-sec.butyl-4-alpha-methylbenzylphenol monosulfideBis-2-t-butyl-4-alpha-methylbenzylphenol monosulfideBis-2-n-hexyl-4-alpha-methylbenzylphenol monosulfideBis-2-cyclohexyl-4-alpha-methylbenzylphenol monosulfide'BiS-Z-tt-octyl-4-alpha-methylbenzylphenol monosulfideBis-2-ethyl-4-alpha, alpha-dimethylbenzylphenol monosulfideBis-2-cyclopentyl-4-alpha,

monosulfide Bis-2,4-di-alpha-methylbenzylphenol monosulfide Bis-2-alpha,alpha-dimethylbenzyl-4-alpha, alpha-dimethylbenzylphenol monosulfidealpha dimethylbenzylphenol One hundred and fifty grams (1 mole) of4-t-butylphenoland 104 g. (1 mole) of styrene were used in thisreaction. To a slurry prepared using one-fifth of each reactant therewas added 1.5 g. conc. sulfuric acid, as catalyst. The remainder of thereactants were added over a period of 2 hours while the reacting masswas maintained at 50 to 60 C. The reaction mixture was allowed to standovernight and the catalyst was removed by washing. On distillation 72.5g. of 2-alpha-methylbenzyl-4-tbutylphenol, B. P. 180 to 185 C. at 5 mm.,was obtained. A solution of 25.4 g. of this product in 100 ml. ofn-hexane was allowed to react with 5.4 g. SO1 to give 26.3 grams ofbis-2-alpha-methylbenzyl-4-t-butylphenol monosulfide, a viscous yellowliquid.

EXAMPLE 2 One mole each of 4-t-amylphenol and styrene were similarlyreacted, using 8.0 g. conc. H 80 This yielded 66 g. of2-alpha-methylbenzyl-4-t-amylphenol. B. P. 185 to 190 C. at 5 mm. Asolution of 26.8 g. of this phenol in 100 ml. of n-hexane was treatedwith 5.4 g. of S01 followed by removal of the solvent. This yielded 28.4g. of bis-alpha-methylbenzyl-4-t-amylphenol monosulfide, a clear lightyellow liquid.

EXAMPLE 3 One hundred sixty-two g. p-cresol (1.5 moles) and 20 g. SnClcatalyst, were placed in a 500 ml. flask. One hundred fifty-six g.styrene (1.5 moles) were added with stirring over a one-hour period atto 70 C. After heating the reaction mixture 3 hours at 65 to 70 C., itwas Washed with dilute hydrochloric acid ml. conc.

HCl plus 300 ml. water), 200 ml. 5% NaOH, and finally with water. Theproduct was vacuum distilled. The yield was 152 g. ofalpha-methylbenzyl-4-methylphenol boiling at to C. at 10 mm. Sulfurdichloride EXAMPLE 4 Ninety-three grams of 4-alpha-methylbenzylphenol,obtained by styrenating phenol, was reacted with 56 g. diisobutylene inthe presence of 5 g. of cone. H 80 at 30 to 35 C. for 4 hours. Thisyielded 99.5 g. of 2- tt-octyl-4-alpha-methylbenzyl phenol. B. P. was180 to 185 C. at 10 mm. Reacting 25 g. of this with 4.4 g. SCI in asolvent such as hexane, bis-2-tt-octyl-4-alphamethylbenzylphenolmonosulfide is obtained as a viscous yellow liquid.

EXAMPLE 5 For the preparation of 2,4-di-alpha-methylbenzylphenol, 94 g.phenol (1 mole) and 38 g. cone. H 80 were placed in 500 ml. flask. Then208 g. styrene were introduced with stirring during 1 hr. 55 min. at 25to 27 C. The reaction mixture was stirred at 25 C. for 2 hrs. afteradding 1.9 g. additional cone. sulfuric acid. One hundred ml. of waterwere added and the mixture was stirred while heating on the steam bathto 75 to 80 C. The aqueous layer was removed in a separatory funnelafter addition of petroleum ether to facilitate separation. Thepetroleum ether was removed on a steam bath and the residue wasdistilled under reduced pressure. The 2,4-dialpha-methylbenzylphenol, acolorless liquid, was taken at 190 to 200 C. at 1 mm. It weighed 129.5g. By reacting 25 g. of 2,4-di-alpha-methylbenzylphenol with 4.5 g. SClin the absence of solvent, 25.1 g. ofbis-2,4-di-alpha-methylbenzylphenol monosulfide was obtained as aviscous, yellow liquid.

The inhibiting eifect of the antiozone agents in rubber was determinedby treatment of unaged, cured stocks with air of controlled low ozonecontent in specially designed equipment and also by outdoor exposure tonatural weathering. The tests were conducted with onehalf inch dumbbellsamples of approximately 100 gauge thickness. The special apparatus fortesting with air of contIolled low ozone content and the method oftesting therein are described in the articles by Ford and Cooper,appearing in India Rubber World for September and October 1951, entitledA Study of the Factors Affecting the Weathering of Rubber-likeMaterials-I and II. The following reports of such tests give the ozoneconcentration maintained during each test in parts per 100,000,000 partsof air, the duration of the test, and the temperature used. Two types oftests were conducted. In one type-called the dynamic testthe sample wasrepeatedly stretched between the limits of and 20 percent elongation atthe rate of 108 cycles per minute. In the other type of test-the statictest-the samples were stretched 12.5 percent and maintained at thatelongation throughout the test. No special lights were used in eithertest. On completion of each test, the size of the cracks in each samplewas compared visually with the size of the cracks in a blank whichcontained no antiozone agent and which was cured and tested at the sametime as the test sample. The size was determined according to anarbitrary scale of measuring, using the numerals 0, 1, 2, 3, 4 and 5 torepresent no visual cracking and cracks which were very fine, fine,medium, coarse, and very coarse, respectively.

The reported results include data on the tensile properties of the curedrubber stocks before and after aging 2 days in an oven at 212 F. Themodulus and tensile strength are given in pounds per square inch and theelongation is reported as percent of stretch at the break. These dataare included to show that the antiozone agents have no substantialdeleterious effect on the cure or upon the aging of the cured stocks.

The antiozone agents were tested in white stock such as might be used inwhite sidewalls for tires, and also in stock such as that which might beused in tire treads. The blanks of the white stock were compoundedaccording to the following formula:

Parts by weight Natural rubber White pigment and filler 90.2 Stearicacid 1.2 Sulfur 3.0 Accelerator 0.9

All blanks and test samples of white stock were cured 60 minutes at 280F.

The blanks used for testing the effect of the antiozone agents in treadstock were compounded according to the following formula:

All blanks and'test samples of tread stock were cured 45 minutes at 280F.

In all of the test samples, both those tested in the special apparatusand those subjected to natural outdoor weathering, 2.0 parts by weightof the antiozone agent was added to the blank formula for each 100 partsby weight of the rubber present. Any relatively small amount can beemployed, and this can vary, for example, from 0.2 part by weight to 10parts by weight, depending upon the use to be made of the rubbercomposition.

The following tables record the properties of white stocks and treadstocks containing inhibitors of this invention and show that theinhibitors have no substantial effect on the vulcanization or aging ofthe rubber, and give the results of testing the various unaged curedstocks with ozone in the special apparatus described previously.

Table 1.White stock Blank 195. 3 195. 3 195. 3 BiS-2-alphamethylbenzyl-4 methylphenol monosulfide 2 Bis-2-alpha-methylbenzyl -4-t-amylphenolmonosulfide 2 Normal tensile properties:

400% modulus 925 Tensile strength Elongation at; break 635 63 630 Aged 2days in oven at 212 F.:

400% modulus 375 725 675 Tensile strength 625 2, 000 1, 750 Elongationat break. 480 590 570 03in; )efleets (7 hrs. at 60 p. p. h. m. and

Static 4+ 1 2- Dyn amin 4+ 1- 1- Table 2.Whzte stock Blank 195. 3 195. 3Bis-2-a1pha-methylbenzyl-4-sec.amylphenol monosnl fid a 2 Normal tensileproperties:

400% modulus 875 Tensile strength 3, 465 Elongation at break 605 Aged 2days in oven at 212 F.:

400% modulus 900 1, 000 Tensile strength 2, 2, 100 Elongation at break545 530 Ozone effects (7 hrs. at 60 p. p. h. m. and 95 F.):

Static 4 0+ Dynamic 4- 0+ Table 3.White stock Table 8.Tread stock BlankI 195.3 195. 3 Blank 15512 155.2Bis-2-tt-octyl-4-alpha-methylbenzyl-phenol mono-Bis-2,e-di-alpha-methylbenzylphenol monosulfide 2 sulfide 2 Cured 46min. at 280 F. Normal tensile properties: Normal tensile properties:

400% modulus 925 825 0% modulus 2, 750 2, 425 Tensile strength--- 3, 325Tensile strength 4, 275 4, 275 Elongation at break 635 630 Elongation atbreak. 525 560 Aged 2 days in oven at 212 F; I Aged 2 days in oven at212 F.:

400% modulus 376 750 400% moduluq 2, 640 Tensile strength 625 1,875Tensile strength 2, 715 480 555 1 0 Elongation at break 410 Ozoneefieets (14 hrs. at 25 4+ 2+ perature): 4+ 1 Static 3- 1+ Dy'narnir' 30+ The foregoing results show the inhibiting eifect of the antiozoneagents of this invention, and that they have no substantial elfect onthe vulcanization of the 195 3 195 3 rubber or no deleterious efiect onthe aging of the vulcanizate. The following tables show the effect of 2the inhibitors in white and tread stocks exposed to 3 32g 3 23% naturalWeathering. E ga on at e '6 5 '63 Table 9.Evaluati0n of white stocksafter outdoor aging Aged 2 days in oven at 212 400% modulus 900 925Tensile strength 2, 150 2, 225 After days Elongation at'break.-. 545 54525 Ozone effects (7 hrs. at 60 p. p.

Static 4 0 Front Back Edge Dyn amip 4- 0-}- Blank 5 2- 5- Bis 2 alphamethylbenzyl 4 -methylphenol so u l fi "lulu Tn 1'11"1' 1+ 3 15- -a pa-me y enzy -amy p eno Table 5 .-T read stock monosulfide -l 3+ 1+ 3+Blank I55. 2 155. 2 Table 10.--Evaluation of white stocks after outdoorBEialphajnethylbenzyl-4-rnethylphenol monosul; I v 2 exp osure N orlrlstensiefilropertiesz 2 600 mo us Ten ile strength 4: 250 Mter 20 daysA dl llzo gation at breatgkzfli fi 525 545 ge ays in oven 9. 1

400% modulus 2, 525 Front Back Edge Tensile strength 2, 650 Elongationat break 415 0 Blank 4 1+ 4 igig fig l (14 at 25 and roomBis-2-a1pha-nlethylbenzyl-l-sec. amylphenol Statm V V 0 monosulfide 2 l3 Dynamic 3 0 Table 11.Evaluation of white stocks after outdoor exposureTable 6.Tread stock After 30 days Blank 155.2 155. 2 155; 2 F 1; Back Ed6 Bis-2-alpha-methylbenzyl-4-t-butylphenol m g monosulfide 2Bis-Z-alpha-methylbenzyl-4-t-arny1phenol Blank 5 2 5 g 2 Bis2-tt-oegyl-4-alpha-methylbenzylphenol 3 400% modulus 2,700 2, 500 2,425monosum e ti t tii-t '25? %28 Z18 onga 1011 a rea Aged 2 days in oven at0 Table 12. Evaluatzon of whzte stocks after outdoor 400% modulusexposure Tensile strength 1, 450 1, 850 1, 950 Elongation at break. 295350 375 Ozone efieets (14 hrs. at 25 p. p. Aft 3 days temperature)Static-. 2 1 0 Dynamic Front Back Edge Blank 4 1+ 4 Bis 2 -mflegwl 4alpha lnethylb enzylphenol 2 1 2 Table 7.'Tread stock moms de Tabl13.-Evaluation o tread stocks a ter outdoor Blank 156. 2 155. 2 e f fBigg-tt-octyM-alpharmethylbenzylphenol monosul- 2 exposure e Normaltensile properties:

400% modulus 2, 650 2, 500 After 30 days Tensile strength 4, 200 4,050Elongation at break 525 535 I Aged 2 days in oven at 212 F.: Front Back400% modulus i 2, 400 Tensile strength.-. 2, 475 Elongation at break 355405 Blank 2- 2- Ozone effects (14 hrs. at 25 p. p. h.'m. and room tem-Bis-2-a1pha-methylbenzyl-et-t-anlylphenol perature): flde 4. 1 1-Static. 3+ 1 Bis-2-alpha-methylbenzyl-4-t-butylphenol Dy 3 1- fide 1 1Table 14.Evaluatin of tread stocks after outdoor exposure After 30 daysFront Back Blank 2 1+ iit i iliffYflflfftlliifflflitiiilffffffff l 1 1Table 15.Evaluation of tread stocks after outdoor Table 16.Evaluation oftread stocks after outdoor exposure After 30 days Front Backfilifi-arsisn aman anesea'sia anrejjjji i+ i The recorded results areillustrative. The antiozone agents can be used in rubber compositionscompounded for use in tires and for latex compositions compounded foruse in rubber thread and in other rubber stocks.

By sulfur vulcanization is meant the curing of rubber by reaction witheither free sulfur or a vulcanizing agent of the sulfur-donor type.Known agents of the latter type include the various phenol polysulfidesincluding the alkyl derivatives thereof, the Xanthogen polysulfides, thethiuram disulfides and polysulfides, various amine sulfides includingdialkylamine polysulfides and reaction products of primary amines withexcess sulfur. Known vulcanization accelerators are useful in speedingup the vulcanization process and are operative herein, especially therelatively active accelerators including the thiazole sulfenamides, e.g. N-cyclohexyl-2-bonzothiazolesulfenamide, thiazoline sulfenamides,thiocarbamyl sulfenamides, mercaptothiazoles, mercaptothiazolines,thiazolyl monoand di-sulfides, the N,N-dialkyl-dithiocarbamates, thethiuram sulfides, the xanthogen sulfides, metallic salts ofmercaptothiazoles or mercaptothiazolines or dithiocarbamic acids. One ormore accelerator activator is often used with any of the acceleratorsmentioned, and such activators include the various derivatives ofguanidine known in the rubber art, amine salts of inorganic and organicacids, various amines themselves, alkaline salts such as sodium acetateand the like, as well as other activators known to the art.Additionally, two or more accelerators or accelerator combinations aresometimes desirable in a single rubber compound. Many of theaccelerators mentioned above are suitable in latex formulation,especially such common accelerators as piperiidiniumpenetamethylenedithiocarbamate, zinc butylxanthate, zinc ethylxanthate,zinc salt of mercaptobenzothiazole, zinc dimethyldithiocarbamate, andzinc dibutyldithiocarbamate. Although vulcanization is usuallyaccomplished by heating a vulcanizable rubber composition at atemperature in the range of 240 to 400 F. for a time ranging fromseveral hours to a few seconds, vulcanization does take place at lowertemperatures such as ordinary room temperature. It is quite common tovulcamm a latex film containing an ultra accelerator by allowing thefilm to remain at room temperature for several hours or a few days.

This application is a continuation-in-part of my application S. N.400,346, now abandoned, and a continuation of application S. N. 400,347of Lloyd 0. Bentz and mystelf, now abandoned.

What I claim is:

1. A sulfur-vulcanized composition of natural rubber which contains asmall amount of bis-2,4-disubstituted phenol monosulfide in which onesubstituent is an alphamethylbenzyl group and the other substituent isfrom the class consisting of alkyl, cycloalkyl and aralkyl groupscontaining up to nine carbon atoms.

2. A sulphur-vulcanized composition of natural rubber which contains asmall amount of a bis-2-alpha-methylbenzyl-4-amylphenol monosulfide.

3. A sulfur-vulcanized composition of natural rubber which contains asmall amount of bis-2-alpha-methylbenzyl-4-methylphenol monosulfide.

4. The process of sulfur-vulcanizing a natural rubber composition whichcomprises vulcanizing such composition in the presence of a small amountof a bis-Z-alphamethylbenzyl-4-amylphenol monosulfide.

5. The process of sulfur-vulcanizing a natural rubber composition whichcomprises vulcanizing such composition in the presence of a small amountof bis-Z-alpha methylbenzyl-4-methylphenol monosulfide.

6. A sulfur-vulcanized composition of natural rubber which contains asmall amount of a bis-2-substituted-4- alphamethylbenzylphenolmonosulfiide in which the Z-substituent is from the class consisting ofalkyl, cycloalkyl and aralkyl groups which contain up to nine carbonatoms.

7. A sulfur-vulcanized composition of natural rubber which contains asmall amount of bis-2-methyl-4-alphamethylbenzylphenol monosulfide.

8. A sulfur-vulcanized composition of natural rubber which contains asmall amount of a bis-2-octyl-4-alphamethylbenzylphenol monosulfide.

9. A sulfur-vulcanized composition of natural rubber which contains asmall amount of bis(2,4-di-alpha-methy1- benzylphenol)monosulfide.

10. The method of sulfur-vulcanizing a natural rubber composition whichcomprises vulcanizing such a composition in the presence of a smallamount of a bis-2,4-disubstituted phenol monosulfide in which onesubstituent is an alpha-methylbenzyl group and the other substituent isfrom the class consisting of alkyl, cycloalkyl and aralkyl groups whichcontain up to nine carbon atoms.

11. The method of sulfur-vulcanizing a natural rubber composition whichcomprises vulcanizing such a composition in the presence of a smallamount of bis-Z-methyl- 4-alpha-methy1benzylphenol monosulfide.

12. The method of sulfur-vulcanizing a natural rubber composition whichcomprises vulcanizing such a composition in the presence of a smallamount of a bis-2-octyl-4- alpha-methylbenzylphenol monosulfide.

13. The method of sulfur-vulcanizing a natural rubber composition whichcomprises vulcanizing such a composition in the presence of a smallamount of bis-2,4-di-alphamethylbenzylphenol monosulfide.

14. The process of sulfur-vulcanizing a natural rubber composition whichcomprises vulcanizing such composition in the presence of a small amountof a bis-2,4-disubstituted phenol monosulfide in which one substituentis an alpho-methylbenzyl group and the other substituent is from theclass consisting of alpha-methylbenzyl, alkyl, cycloalkyl and aralkylgroups containing up to nine carbon atoms.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,849,517 August 26, 1958 Harry E. Albert It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

' In the heading to the printed specification, line l, in the. title ofinvention, for PORCESS"- read PROCESS column 3 line 16, after "in"insert a column 4 "Table 1, first column thereof,v third line from thebottom, for "95 F;" read 95 F. column 7 line 49, for"2-bonzothiazol'esulfenJ read 2- benzothiazolesulfencolumn 8, line 9,for "stelf read self line 17 for "sulphurvulcanized" readSlllIElIP-Vl110fil'll26dline 33 for F'alphamethylbenzylphenolmonosulfiide" read alphamethylb'enzylphenol monosulfide line 68, for"alpho-" read alpha- Signed and sealed this 27th day of September 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT c. WATSON Attesting Officer Conmiuioner of Patent

1. A SULFUR-CULCANIZED COMPOSITION OF NATURAL RUBBER WHICH CONTAINS ASMALL AMOUNT OF BIS-2,4-DISUBSTITUTED PHENOL MONOSULFIDE IN WHICH ONESUBSTITUENT IS AN ALPHAMETHYLBENZYL GROUP AND THE OTHER SUBSTITUENT ISFROM THE CLASS CONSISTING OF ALKYL, CYCLOALKYL AND ARALKYL GROUPSCONTAINING UP TO NINE CARBON ATOMS.